Combining Very Large Quadratic and Cubic Nonlinear Optical Responses in Extended, Tris-Chelate Metallochromophores with Six π-Conjugated Pyridinium Substituents

• Published in: Journal of the American Chemical Society Vol. 132; no. 10; pp. 3496 - 3513
• Main Authors: Coe, Benjamin J, Fielden, John, Foxon, Simon P, Brunschwig, Bruce S, Asselberghs, Inge, Clays, Koen, Samoc, Anna, Samoc, Marek
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 17.03.2010; Amer Chemical Soc
• Subjects: 2,2'-Dipyridyl - analogs & derivatives; 2,2'-Dipyridyl - chemistry; Chelating Agents - chemical synthesis; Chelating Agents - chemistry; Chemistry; Chemistry, Multidisciplinary; Crystallography, X-Ray; Electrochemistry; Ferrous Compounds - chemistry; Magnetic Resonance Spectroscopy - methods; Models, Molecular; Nonlinear Dynamics; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Physical Sciences; Pyridinium Compounds - chemical synthesis; Pyridinium Compounds - chemistry; Ruthenium - chemistry; Scattering, Radiation; Science & Technology; Spectrophotometry, Ultraviolet - methods; TERAHERTZ-WAVE GENERATION; METAL-TO-LIGAND; HIGH-FREQUENCY DEMODULATION; CHARGE-TRANSFER STATES; ORGANOMETALLIC COMPLEXES; ELECTROABSORPTION SPECTROSCOPY; HYPER-RAYLEIGH SCATTERING; 2-PHOTON ABSORPTION PROPERTIES; DIPOLAR RUTHENIUM(II) COMPLEXES; IONIC OCTUPOLAR MOLECULES
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja910538s

We describe a series of nine new complex salts in which electron-rich RuII or FeII centers are connected via π-conjugated bridges to six electron-accepting N-methyl-/N-arylpyridinium groups. This work builds upon our previous preliminary studies ( Coe B. J. J. Am. Chem. Soc. 2005, 127, 13399−13410; J. Phys. Chem. A 2007, 111, 472−478 ), with the aims of achieving greatly enhanced NLO properties and also combining large quadratic and cubic effects in potentially redox-switchable molecules. Characterization has involved various techniques, including electronic absorption spectroscopy and cyclic voltammetry. The complexes display intense, visible d → π* metal-to-ligand charge-transfer (MLCT) bands, and their π → π* intraligand charge-transfer (ILCT) absorptions in the near-UV region show molar extinction coefficients as high as ca. 3.5 × 105 M−1 cm−1. Molecular quadratic nonlinear optical (NLO) responses β have been determined by using hyper-Rayleigh scattering at 800 and 1064 nm and also via Stark (electroabsorption) spectroscopic studies. The directly and indirectly derived β values are very large, with the Stark-based static first hyperpolarizabilities β0 reaching as high as ca. 10−27 esu, and generally increase on extending the π-conjugation and enhancing the electron-accepting strength of the ligands. Cubic NLO properties have also been measured by using the Z-scan technique, revealing relatively high two-photon absorption cross sections of up to 2500 GM at 750 nm.